Heterogeneous Pore Distribution Research Articles

Grain size prediction for stainless steel fabricated by material extrusion additive manufacturing

Most traditional powder melting-based additive manufacturing (AM) technologies generally yield high-performance parts at the expense of additional cost and energy consumption. As an economical and efficient alternative method, material extrusion (ME) that deploys polymer-based filaments with highly filled metal particles offers the possibility of scalable, low-cost fabrication of metal components. As a critical step, sintering governs the mechanical strength and geometry of the final parts. The grain growth behavior induced during sintering should be well controlled to achieve the parts with the desired mechanical performance. Due to the nature of AM, grain growth kinetics could also involve extremely complex grain boundary migration and atomic diffusion mechanisms caused by the heterogeneous pore distribution. In this work, an analytical model was developed to predict and understand the grain growth behavior of stainless steel (SS) 316L built by ME-based sintering-assisted AM. Such a model accounts for anisotropic viscosity parameters calibrated through a three-dimensional dilatometry test, enabling the prediction of grain size evolution during sintering. Grain growth kinetic parameters were further identified by the grain size data at the heating and holding stages. To validate and generalize the model, we also conducted the grain size evolution prediction under different sintering temperature profiles for as-built SS 316L specimens. This work will provide scientific insights into the grain growth behavior of metal parts built by this AM technique and its understanding can be readily transferred to other sintering-assisted AM processes like binder jetting and ink writing for metal structure creation.

Preparation and characterization of potato crust-based polyurethane Foam-II

In this research study, environmentally friendly and biodegradable PU polymer foam was synthesized from starch-containing potato crust to be used as a thermal insulation material by reducing reliance on fossil resources and utilizing biomass resources. Biopolyols were obtained by reacting with active solvents at different reaction times, in the presence of different catalysts and at different catalyst concentrations. The most suitable polyol in terms of biomass content, density, viscosity and acid-hydroxyl number was selected for PU foam synthesis. Reactions for PU synthesis were tried and PU foam was synthesized. The synthesized PU foam was examined by Scanning Electron Microscope (SEM) and Thermo Gravimetric Analysis (TGA). Its morphological structure, thermal degradation properties, sound transmission coefficient and water absorption properties were determined by comparing it with a commercial PU foam. SEM images showed a heterogeneous pore distribution with closed and open cells, the majority of which were closed. From the TGA results, it was determined that a two-step degradation occurred and incorporating biomass into its structure improved the total thermal degradation properties. The sound transmission rate of starch-containing PU foam, when used as a thermal insulation material, was measured to be lower than the concrete structure, but partially close to and higher than that of commercial PU foam. The water absorption properties of the synthesized PU foam were found to be significantly higher compared to commercial PU foam and and contributed to its usability as a thermal insulation material. Thermal insulation material PU foam is synthesized in terms of its properties.

On the dissolution paths and formation mechanisms of paleokarst reservoirs: Constraints from reactive transport modeling

Paleokarst is widespread in ancient carbonate rocks and is often related to hydrocarbon reservoirs, but the physico-chemical mechanism of forming such paleokarst reservoir remains poorly understood due to the complexity of meteoric water–rock interactions and a lack of geological research methods other than petrological analysis. Here, we implement the reactive transport modeling approach and reconstruct the dynamic evolution of the fluid–mineral–porosity system during paleokarst processes. In an eogenetic karst system, the early dissolution path is dominated by relatively uniform and diffuse dissolution in intergranular pores. The dissolution path then gradually transitions to preferential dissolution in local high-permeability zones, resulting in spongy dissolution. This is interpreted as the result of a combination of a heterogeneous initial pore distribution and the positive feedback between increasing flow and increasing dissolution. A higher degree of porosity heterogeneity and the presence of penecontemporaneous microfractures could facilitate the formation of preferential flow and spongy karst systems. Comparative simulations of eogenetic and telogenetic karst systems show different dissolution paths, formation mechanisms and distributions of hydrocarbon reservoirs, i.e., intergranular pore-dominated eogenetic karst with high mobility and high reactivity characteristics versus tectonic fault/fracture-dominated telogenetic karst with high mobility and low reactivity characteristics. The results provide a better general understanding of the water–rock interactions in meteoric diagenetic environments, and they indicate that hydrocarbon exploration should concentrate on carbonate shoals/mounds in the structural slope break zones associated with syngenetic faults, paleo-uplifts/highlands, and platform margins to identify high-quality eogenetic karst reservoirs and on tectonic fault/fracture systems and the lower parts of the high-permeability layers connected by these faults/fractures to identify high-quality telogenetic karst reservoirs.

An improved anisotropic continuum model for the flow and heat transfer in grain aeration system

AbstractTo investigate the influence of pore structure distribution on the flow and heat transfer during the aeration process of a grain pile, an anisotropic continuous model (ACM) was developed based on the homogeneous continuous model (HCM). The improved ACM includes spatial resistance factors and effective thermal conductivity correction coefficients. The experimental results were compared with the particle‐resolved computational fluid dynamics (PRCFD) and ACM simulation results to verify the accuracy. At higher inlet velocities, the HCM underestimated the pressure drop in the wheat fixed bed, with an average deviation of 21%. In contrast, the improved ACM incorporates the effect of resistance factors and had an average deviation of less than 10% from the experimental. By simulating the pilot‐scale bin aeration system, the accuracy of the improved ACM applied to the real bin was ensured, considering the change in the porosity of the grain pile along the center of the bin to the bin wall and the grain pile height direction. The range of variable porosity distribution was set at .35–.45, and the total average deviation between the ACM simulation static pressure and the experimental value was 9.7% when the inlet airflow velocity was .019 m/s. The simulated temperature of the ACM matches the measured temperature better compared to the temperature values of the grain pile at different heights in the HCM with a constant porosity of .45. Therefore, the impact of four central air collection duct forms on airflow and temperature was discussed, and it was determined that the pipe with a larger diameter at the top and a smaller diameter at the bottom air collection duct was more advantageous when used in a horizontal aeration system by applying the improved ACM to different scenarios.Practical ApplicationsThis study introduces the resistance factor and effective thermal conductivity in a laboratory‐scale fixed bed of wheat. An improved anisotropic continuous model was established for simulating the flow and heat transfer in the fixed bed during the aeration process. The improved anisotropic continuous model accurately reflected the non‐uniformity of fixed bed flow and temperature transfer in the fixed bed. This model can be employed for simulating flow and heat transfer in large‐scale actual storage systems characterized by heterogeneous pore distribution, while ensuring appropriate computational efficiency and precision.

Anisotropic sintering shrinkage behavior of stainless steel fabricated by extrusion-based metal additive manufacturing

Metal additive manufacturing (AM) can be achieved by first extruding polymer-based filaments with densely filled metal particles to create the so-called ‘green’ parts and then experiencing debinding and sintering to produce finished metal components. As a critical step, sintering governs the shape dimension, relative density, and resultant strength of final parts. Thus, there is a growing need for research on understanding and quantifying the sintering-induced anisotropic shrinkage. In this work, the underlying behaviors of anisotropic shrinkage during the entire sintering of extrusion-printed stainless steel 316L parts will be understood and quantified through a combination of theoretical study and experimental investigations including three-directional dilatometry, scanning electron microscopy, and X-ray computed tomography. The three-dimensional size evolution of ‘brown’ parts before sintering will be studied through a macroscopic analysis of shrinkage anisotropy factors and microstructure characterizations. Different filling strategies will be integrated with initial pore distribution characterization for anisotropic dimensional change analysis. The heterogeneous pore distribution will be discussed in conjunction with the anisotropic viscous behavior to eventually unveil the shrinkage performance in the course of sintering. The findings of this work will provide insights into the anisotropic sintering mechanisms and fill the knowledge gap of the relations between extrusion-based metal AM process and sintered structures of metal alloys.

Multiple upscaling procedures for gas transfer in tight shale matrix-fracture systems

Multiple upscaling schemes for gas transfer in nanoporous media, microporous matrix, core-scale matrix, and centimeter-scale matrix-fracture systems are investigated. An Open Multi-Processing (OpenMP)-based parallelized multi-scale numerical solver for micro-gaseous flow in composite microporous media is developed by coupling the pore-scale multiple-relaxation-time lattice Boltzmann method (MRT-LBM) and representative elementary volume (REV)-scale LBM model. The permeability of the microporous matrix is calculated through hundreds of pore-scale simulations for gas transfer in nanoporous media, before being imported into the REV-scale LBM to predict the core-scale matrix permeability. It is followed by the investigations of the variations of core-scale permeability with the heterogeneous spatial distribution of organic matter aggregates, mineral aggregates, interparticle pores, and microfractures. The parallel and sequential gas transfer processes in a larger shale system containing the tight matrix and hydraulic fractures are studied and analyzed. The results reveal several new insights: 1) the microscale spatial distribution of multiple constituents has relatively little effect on the core-scale permeability; 2) an ultra-large local pressure gradient occurs in a thin boundary layer of tight shale matrix, which is shown to be proportional to the square root of the permeability ratio, resulting in considerable flow characteristic velocity in the matrix; 3) the in-situ matrix-fracture transfer satisfies a sequential transport process due to a long equilibration time delay between the tight matrix and fractures; 4) the observed high production rate for tight shale may be caused by the ultra-large local pressure gradient in the matrix (and not by a large apparent permeability as commonly assumed). The results also reveal some anomalous phenomena for multiscale gas transfer in tight shale formations.

Performance improvement of lateral flow assay using heterogeneous nitrocellulose membrane with nonuniform pore size

Lateral flow assay (LFA) has found widespread applications in point-of-care diagnostics over the past decades. Its detection sensitivity is dependent on the properties of paper itself (e.g., porous microstructure of nitrocellulose membrane), however, the effect remains unknown. Existing mathematical models for LFA have not been proved to predict the variation trends of detection performance with different specifications of nitrocellulose membrane. To address this, we developed a mathematical model coupling the macroscopic capillary flow and the binding reaction on the internal pore surface to illustrate the complex interaction among the convection, diffusion, and binding reaction with different nitrocellulose membranes. The model was experimentally validated by implementing nucleic acid detection on LFA. The simulated results suggest that due to the trade-off between the reagent transport and the reactive surface area, there is an optimal average pore size of the nitrocellulose membrane to achieve the highest detection sensitivity. Additionally, a heterogeneous pore distribution design (i.e., smaller pore diameter at the test line region and larger pore diameter for the rest region) of the nitrocellulose membrane was proposed to provide a faster detection with improved sensitivity. The numerical model would be a practical tool for the material selection and optimization of LFA.

Design and mechanical properties analysis of heterogeneous porous scaffolds based on bone slice images.

Bone tissue engineering plays an extremely important role in the clinical treatment of bone defects. Porous scaffold is one of the three essential factors of bone tissue engineering, and its structural design has attracted more and more attention . At present, most of the design methods of porous scaffolds focus on uniform porous scaffolds with periodic and regular pore structures. However, periodic and regular pore structure cannot comprehensively and accurately simulate the microstructures and mechanical properties of natural bone. To address this problem, based on bone slice images and VT (Voronoi-Tessellation) method, this article proposed a design method of HPS (Heterogeneous Porous Scaffolds) with bionic pore structure and controllable porosity. The FDM (fused deposition modeling) printing technology was applied to fabricate HPS with different porosities, and the mechanical properties of the HPS were analyzed by experiments. The research results illustrate that the HPS constructed by the design method proposed in this article have good controllability, and their internal pore structures are highly similar to those of natural bone, which have biomimetic characteristics. The mechanical property analysis illustrate that the stiffness and compressive strength of HPS decrease with the increase of porosity, in addition, the heterogeneous pore distribution makes HPS have the characteristics of non-concentrated and discontinuous damage distribution. This study provides a new idea for the design of porous scaffolds and a theoretical basis for the bionic design of HPS.

Heterogeneities and defects in powder compacts and sintered alumina bodies visualized by using the synchrotron X-ray CT

The uniaxial die compaction and sintering is an important industrial production method for metal and ceramic components. While submicron- and nano-sized powders are finding increasing use for making dense materials with finest grain sizes, the uniformity of microstructure, and then, the reliability of the products depend on the heterogeneity in powder packing structure. Here we applied the synchrotron X-ray multiscale-CT to characterize the complex domain structures, i.e., agglomerates, in powder compacts, and revealed how heterogeneous distribution of fine residual pores is formed by the differential sintering of agglomerates by using a submicron alumina powder as a model. A crack-like defect was identified as the largest defect. This defect was formed along the boundary between a plate-shaped agglomerate and its surroundings. A technique was also proposed to visualize the heterogeneous distribution of residual pores by using SEM. These characterization methods will open up new possibilities for the optimization of ceramic processing.

Study of the Utilization of Spent Grain from Malt Whisky on the Quality of Wafers

This study aimed at determining the quality parameters of the wafer formulated with the addition of grain spent (SG), resulting from the obtainment of whisky. In this sense, wafers were formulated from chickpea flour, spent grain, wild garlic paste, golden flaxseed, and hemp seeds. These food products were analyzed in terms of texture, density, and pH of the batter, but also of the final product for proximate analysis, baking loss, texture, water activity, color, antioxidant capacity, water holding capacity and oil holding capacity, microstructure, and sensorial analysis. The addition of spent grain in the wafer formulation led to products with a high acceptability, the texture of the batter underwent changes due to the addition of spent grain, all parameters increased, and only adhesiveness decreased. The density and pH of the samples with SG decreased. The fracturability of the products with SG decreased with the addition of SG compared to the control sample, and the color becomes darker, influenced by the specific color of the SG. With the addition of spent grain, it increases the fiber and protein content, the antioxidant capacity, but also the baking loss due to the fibers contained in it. The microstructure of samples with the addition of SG shows a heterogeneous distribution of pores on the cross section of the samples, with larger pores in the center of the wafer samples.

Design and analysis of the mechanical properties of controllable porous scaffolds for bone tissue engineering.

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Multiscale correlated analysis of the Aguas Zarcas CM chondrite

AbstractIn this paper, we report the results of a campaign of measurements on four fragments of the CM Aguas Zarcas (AZ) meteorite, combining X‐ray computed tomography analysis and Fourier‐transform infrared (FT‐IR) spectroscopy. We estimated a petrologic type for our sampled CM lithology using the two independent techniques, and obtained a type CM2.5, in agreement with previous estimations. By comparing the Si‐O 10‐µm signature of the AZ average FT‐IR spectra with other well‐studied CMs, we place AZ in the context of aqueous alteration of CM parent bodies. Morphological characterization reveals that AZ has heterogeneous distribution of pores and a global porosity of 4.5 ± 0.5 vol%. We show that chondrules have a porosity of 6.3 ± 1 vol%. This larger porosity could be inherited due to various processes such as temperature variation during the chondrule formation and shocks or dissolution during aqueous alteration. Finally, we observed a correlation between 3D distributions of organic matter and mineral at micrometric scales, revealing a link between the abundance of organic matter and the presence of hydrated minerals. This supports the idea that aqueous alteration in AZ’s parent body played a major role in the evolution of the organic matter.

Synthesis and Characterization of Activated Carbon from Agrowastes for the Removal of Acetic Acid from an Aqueous Solution

In this study, activated carbons prepared from agrowastes by chemical activation were used to remove acetic acid from an aqueous solution through a batch process. The prepared adsorbents were characterized by SEM, XRD, FT-IR, and point of zero charge (pHpzc). The effects of adsorbent dosage, initial concentration, and contact time were considered. Equilibrium data was tested using Langmuir, Freundlich, Temkin, and Frenkel–Halsey–Hill models. The degree of adsorption of acetic acid increased for both adsorbents as contact time, and adsorbent dosage and initial concentration were increased. The adsorption data were described well by the (Freundlich=Frenkel–Halsey–Hill) models with the highest regression coefficient of [Formula: see text] and [Formula: see text] for Rice Husk Activated Carbon (RH-AC) and Potato Peels Activated Carbon (PP-AC), respectively. This suggests a multilayer through the existence of a heterogeneous pore distribution in the adsorbent surface. Kinetic data agreed well with pseudosecond-order ([Formula: see text] and [Formula: see text]) RH-AC and PP-AC, correspondingly. This indicates that the adsorption process was chemisorption in nature. The regeneration studies showed that the adsorbents prepared could be renewed and reused before losing their adsorbing affinity for acetic acid.

Volume, strength, and stiffness characteristics of expandable foam grout

An expandable foam grout (EFG) is developed to fill underground cavities. The objective of this study is to evaluate the volume, strength, and stiffness of the EFG during curing using various testing methods. Flow, expansion, and unconfined compressive tests are conducted to investigate the fundamental material properties of the EFG. X-ray computed tomography is performed to verify the pore distribution of the EFG. Elastic waves and electrical resistivity are monitored to estimate the stiffness and strength characteristics of the EFG. The results show that EFG has high flowability, expanding within four hours depending on the temperature. The X-ray computed tomography images indicate a heterogeneous pore distribution in the EFG. A series of relationships between static and dynamic properties based on the elastic wave velocities and electrical resistivity are established. Furthermore, elastic wave measurement and electrical resistivity monitoring may be useful for estimating the volume, strength, and stiffness characteristics during curing.

Adsorptive Stripping Voltammetric Determination of 2,4‐Dichlorophenol by Laponite Modified Carbon Paste Electrode

AbstractA laponite modified carbon paste electrode was prepared, characterized and applied for the 2,4‐dichlorophenol (2,4‐DCP) voltammetric determination. It takes advantage of the ability of laponite to adsorb phenols, as well as of its availability and very low cost. Kinetic and equilibrium data for 2,4‐DCP adsorption by laponite in aqueous dispersions demonstrated that the adsorption process obeyed a pseudo first order kinetic model and was consistent with the formation of adsorbed multilayers on a surface with heterogeneous pore distribution. The composite paste electrode exhibited a heterogeneous surface with 65 % increased surface area and 27 % enhanced catalytic activity compared to the unmodified one. The adsorptive stripping voltammetric determination of 2,4‐DCP at an electrode with an optimized graphite:laponite ratio of 55 : 15 w% using a 3 min accumulation time at pH 5.5 was found to be suitable for its quantification in the linear concentration range extended up to 50 μmol L−1 with a sensitivity of 0.56 μA L μmol−1 and a LOD of 0.2 μmol L−1 (S/N=3).The 2,4‐DCP electrochemical response was not affected by the presence of some structurally similar phenols, like catechol and p‐nitrophenol, while resorcinol, 2‐chlorophenol, and 4‐chlorophenol presented interferences. The results were validated by 2,4‐DCP determination in spiked tap water.

Architectural characterization of Ordovician fault-controlled paleokarst carbonate reservoirs, Tahe oilfield, China

Fault-controlled karst carbonate reservoirs are one of the most important reservoir types in the Tahe oilfield of the Tarim Basin. These reservoirs have a large oil reserve and belong to a strongly reconstructed reservoir type with a highly heterogeneous distribution of pores and fractures. This study characterizes a fault-controlled karst reservoir by using integrated methods, including outcrops, well logging, structure interpretation, seismic inversion, and statistical geomodeling. We have established a fault-/fracture-controlling karstic geologic model and classified the internal architectural elements so that we adopted an origin-controlled hierarchical geomodeling strategy based on the fault-controlling characteristics. The results determined that large strike-slip faults provide an important tectonic framework and that its derived fractures act as important channels and spaces for dissolution. Flower structure fault zones and the associated fractures are the main range of karst development, within which a high stress is concentrated during the strike-slip shear process with a high-density fracture development. This is the highly developed karst reservoir, which mainly is concentrated along large faults. The coexistence of fractures and karst dissolution has resulted in a complicated reservoir architecture (karst architecture), which can be classified into four types: (1) large caverns, (2) small caverns and vugs, (3) fractured zones, and (4) matrix (tight limestone). Controlled by the degree of dissolution, the karst architecture is quite different from the sedimentary facies. Large caverns are formed under the strongest degree of dissolution and are the most favorable reservoir type. Small caves and vugs are created under relatively strong dissolution; they are distributed outside large caves and also can act as favorable reservoirs. The fractured zones are not necessarily affected by strong dissolution but have high conductivity and act as important channels for fluid movement. The carbonate matrix is less reconstructed. The architecture development model of the fault-controlled karst carbonate reservoir presented a tree system, within which the karst reservoir caves are connected by the fractures and faults similar to fruits and trunks. The new geomodeling method revealed the constraining characteristics of faults, seismic attributes, and hierarchical architectural elements. Furthermore, we also have built a 3D model of the Tuoputai unit in the Tahe oilfield to show the robustness of this workflow. This research enables us to better understand the structure of fault-controlled karst reservoirs, and it could provide a specified characterization approach that is considered to be theoretically and practically useful.

The influence of porosity on tablet subdivision

A tablet microstructure, especially the porosity, is a crucial parameter that influences the mechanical properties. Herein, tablet subdivisions were studied as a function of tablet porosity. The tablets were manufactured in the presence of different diluents, namely microcrystalline cellulose, Ludipress®, or lactose monohydrate. Furthermore, the addition of Camphor was investigated, which was thereafter sublimated with a view of obtaining tablets having varying degrees of porosity. Microstructural assays were correlated to the subdivision performance. The increase in porosity reduced the hardness and increased the tablet friability, adversely impacting the subdivision. For all the excipients, an increase in relative porosity >90% represented the threshold level from which an inadequate subdivision occurred. The increase in tablet porosity led to a reduction in mechanical resistance, which, combined with a heterogeneous and discontinuous distribution of pores within the matrix, resulted in poor subdivision results. Controlling tablet porosity is an important consideration when designing tablets having a subdivision purpose.

3D soil void space lacunarity as an index of degradation after land use change

In this work, lacunarity analysis is performed on soil pores segmented by the pure voxel extraction method from soil tomography images. The conversion of forest to sugarcane plantation was found to result in higher sugarcane soil pore lacunarity than that of native forest soil, while the porosity was found to be lower. More precisely, this study shows that native forest has more porous soil with a more uniform spatial distribution of pores, while sugarcane soil has lower porosity and a more heterogeneous pore distribution. Moreover, validation through multivariate statistics demonstrates that lacunarity can be considered a relevant index of clustering and can explain the variability among soils under different land use systems. While porosity by itself represents a fundamental concept for quantification of the impact of land use change, the current findings demonstrate that the spatial distribution of pores also plays an important role and that pore lacunarity can be adopted as a complementary tool in studies directed at quantifying the effect of human intervention on soils.

Hydrophilic Porous Polydimethysiloxane Sponge as a Novel 3D Matrix Mimicking Heterogeneous Pores in Soil for Plant Cultivation.

In this work, a citric acid monohydrate (CAM)-templated polydimethylsiloxane (PDMS) sponge was proposed to mimic heterogeneous pore structures in the soil for plant cultivation. The porosity of the PDMS sponges was tuned by adjusting the CAM template. The water intake capability of the sponge was improved by (3-Aminopropyl) triethoxysilane (APTES) functionalization. The pore size and pore distribution were characterized by SEM and micro-computed tomography (micro-CT). The effect of pore structures on Oryzasativa (O. sativa) growth was investigated. Also, a 3D multi-layer PDMS sponge assembling was proposed to mimic the heterogeneous pore distribution at the different soil depth. The different growth rates of O. sativa and Nicotiana tabacum L. (N. tabacum) seeds on porous PDMS sponge indicated the impact of physical obstacles (pores) and chemical (water content) conditions on plant development. It is anticipated that this PDMS sponge could serve as a 3D matrix to mimic soil and provide a new idea for plant cultivation.

3D soil void space lacunarity as an index of degradation after land use change

ABSTRACT. In this work, lacunarity analysis is performed on soil pores segmented by the pure voxel extraction method from soil tomography images. The conversion of forest to sugarcane plantation was found to result in higher sugarcane soil pore lacunarity than that of native forest soil, while the porosity was found to be lower. More precisely, this study shows that native forest has more porous soil with a more uniform spatial distribution of pores, while sugarcane soil has lower porosity and a more heterogeneous pore distribution. Moreover, validation through multivariate statistics demonstrates that lacunarity can be considered a relevant index of clustering and can explain the variability among soils under different land use systems. While porosity by itself represents a fundamental concept for quantification of the impact of land use change, the current findings demonstrate that the spatial distribution of pores also plays an important role and that pore lacunarity can be adopted as a complementary tool in studies directed at quantifying the effect of human intervention on soils.